In general, a compressor, particularly, a reciprocating compressor has no crankshaft for converting a rotating movement to a linear movement, thereby having small friction loss and so having higher efficiency in compression than that of a general compressor.
In case that the reciprocating compressor is used for a refrigerator or an air conditioner, as a stroke voltage inputted to the reciprocating compressor is varied, a compression ratio of the reciprocating compressor can be varied to control freezing compressor. Such a reciprocating compressor will now be described with reference to FIG. 1.
FIG. 1 is a block diagram showing a structure of an operation control device of the reciprocating compressor in accordance with the conventional art.
As shown therein, the operation control device of the reciprocating compressor includes: a voltage detecting unit 14 for detecting a voltage applied to the reciprocating compressor 13 as the compressor operates; a current detecting unit 12 for detecting a current applied to the reciprocating compressor 13 as the compressor operates; a microcomputer 15 for calculating a stroke by using the voltage detected by the voltage detecting unit 14 and the current detected by the current detecting unit 12, comparing the calculated stroke and a stroke reference value, and outputting a switching control signal on the basis of the comparison result; and a power supply unit 11 for supplying a stroke voltage to the reciprocating compressor 13 by on-off controlling AC power supplied to the reciprocating compressor 13 according to the switching control signal outputted from the microcomputer 15 by using an internal triac (Tr1). Herein, the reciprocating compressor 13 receives a stroke voltage provided to an internal motor (not shown) according to a stroke reference value set by a user and varies an internal stroke so as to vertically move a piston (not shown) in the compressor.
Hereinafter, operations of the operation control device of a reciprocating motor compressor in accordance with the conventional art will now be described.
First, the reciprocating motor compressor 13 receives a voltage supplied to the motor on the basis of the stroke reference value set by a user and varies the stroke so as to vertically move the stroke. Herein, the stroke means a moving distance of a piston in the reciprocating motor compressor 13 in a reciprocating movement.
A turn-on period of the triac (Tr1) of the power supply unit 11 is lengthened by a switching control signal outputted from the microcomputer 15. As the turn-on period is lengthened, the AC power is supplied to the reciprocating motor compressor 13 to drive the reciprocating motor compressor 13. At this time, the voltage detecting unit 14 and the current detecting unit 12 detect a voltage and a current applied to the reciprocating motor compressor 13 and output the detected voltage and current to the microcomputer 15, respectively.
The microcomputer 15 calculates a stroke by using the voltage and the current detected by the voltage detecting unit 14 and the current detecting unit 12, then, compares the calculated stroke with the stroke reference value, and outputs a switching control signal according to the comparison result. That is, when the calculated stroke is smaller than the stroke reference value, the microcomputer 15 outputs a switching control signal for lengthening an on-period of the triac (Tr1) to the power supply unit 11 thereby increasing a stroke voltage supplied to the reciprocating motor compressor 13.
On the other hand, when the calculated stroke is greater than the stroke reference value, the microcomputer 15 outputs a switching control signal for shortening an on-period of the triac (Tr1) to the power supply unit 11 thereby decreasing a stroke voltage supplied to the reciprocating motor compressor 13.
In the conventional art, an over load protector (OLP) 20 for cutting off power applied to. a motor of the compressor 13 when a temperature of the compressor 13 is high or when over current flows in a internal motor of the compressor 13, is installed independent of the operation control device.
Hereinafter, an over load protector (OLP) in accordance with the conventional art will now be described.
The over load protector 20 detects a temperature of a compressor 13 electrically connected with itself. In addition, the over load protector 20 detects heat due to a current flowing therein, and cuts off or passes power applied to an internal motor of the compressor 13 on the basis of a temperature of the detected heat. That is, when a temperature of the compressor 13 gets high, or over current flows in the internal motor of the compressor 13, the over load protector 20 operates to cut off power supplied to the compressor 13, and thus prevents damage of the compressor 13.
However, the over load protector installed in the compressor 13 in accordance with the conventional art cannot be minimized by a size of a power device (not shown) in the over load protector 20, and also, a cost for the compressor increases by installing the over load protector in the compressor.